[llvm] RFC: [TTI] Assume casts between aliasing addrspaces are valid. NFCI. (PR #137969)

[Jay Foad via llvm-commits]

jayfoad wrote:

> I don't think this is the right thing to do, as these should have inverse defaults. We want to assume that all address spaces alias and no addrspacecasts are valid by default. A precise addrspacesMayAlias + isValidAddrSpaceCast will converge to being the same, but if either of them are approximate (including the full conservative default approximation) they will differ.

Fair enough, I can handle this in the target instead: #137986.

https://github.com/llvm/llvm-project/pull/137969